CONTEXT:
It has been suggested that the risk of inpatient psychiatric readmissions is elevated during the postpartum period. To our knowledge, no prior study has compared mothers and nonmothers to determine whether the risk of readmission differs between these 2 groups of women.

OBJECTIVES:
To compare mothers and nonmothers to assess whether childbirth increases the risk for psychiatric readmission and to identify predictors of psychiatric readmission during the postpartum period.

DESIGN:
A population-based cohort study merging data from the Danish Civil Registration System and the Danish Psychiatric Central Register.

SETTING:
The population of Denmark.

PARTICIPANTS:
Two partly overlapping study populations included a total of 28 124 women, 10 218 of whom were mothers, who were followed up from January 1, 1973,through June 30, 2005. Main Outcome Measure Readmission rates to psychiatric hospitals during the 12 months after childbirth (first live-born child).

RESULTS:
The period of highest risk of psychiatric readmission in new mothers was 10 to 19 days post partum (relative risk [RR], 2.71; 95% confidence interval [CI], 1.68-4.37), and the period of lowest risk was during pregnancy (0.54; 0.43-0.69). Childbirth was associated with an increased risk of readmission during the first postpartum month, after which risk for readmission was higher among nonmothers (RR, 1.53; 95% CI, 1.31-1.80). A previous diagnosis of bipolar affective disorder was the strongest predictor of readmissions 10 to 19 days post partum (RR, 37.22; 95% CI, 13.58-102.04). In all, 26.9% of mothers with this diagnosis were readmitted within the first postpartum year.

CONCLUSIONS:
Mothers with mental disorders have lower readmission rates compared with women with mental disorders who do not have children. However, the first month after childbirth is associated with increased risk of psychiatric readmission, and women with a history of bipolar affective disorder are at particular risk of postpartum psychiatric readmissions.